The present disclosure is directed to a method of forming in-situ a boron nitride layer which provides environmental protection for a ceramic matrix composite.
In order to enable composite behavior, ceramic matrix composites (CMCs), such as a silicon carbide-based CMC, require a weak fiber interface coating which typically consists of an amorphous or turbostratic (partially crystalline) boron nitride (BN) inner layer and an outer layer of one or more of silicon carbide (SiC), silicon nitride (Si3N4), boron carbide (B4C), or carbon (C), all of which are deposited by chemical vapor deposition. In terms of stability/reactivity, a more highly crystalline boron nitride phase is desirable and can offer greater protection against molten silicon attack during processing compared to amorphous or turbostratic boron nitride.